The present invention relates to a three-phase cable system comprised of three single-conductor cables each provided with internal water cooling and each provided with a respective cooling-water return-flow pipe.
In laying down fluid-cooled high-power cables, the cooled cable can be provided with one or a plurality of adjoining return-flow pipes for returning the cooling water to a cooling station. In such a case, it is possible, for example, to lay three return-flow pipes parallel to the three cooled cables of the three-phase cable system, with the return-flow pipes being made of high-quality corrosion-resistant steel, each pipe having the same flow cross-section as the cooling-water passage within the respective one of the three single-conductor cooled cables. This expedient appears to be the most advantageous approach with respect to production and installation of the cable system.
In such a set-up, the currents flowing in the cables induce longitudinal voltages in the return-flow pipes; these induced voltages can lead either to unacceptably high surface or contact voltages or else, if the return-flow pipes are grounded at both ends, to unacceptably great energy losses in the power-transmission system.